Recovery processing method of steel balls

Abstract

The invention belongs to the field of metal recovery, and particularly relates to a steel ball recovery treatment method. The steel ball recovery treatment method comprises the following steps: sequentially carrying out first-stage heat treatment and second-stage heat treatment on steel balls with plating layers on the surfaces, quenching to 150-200 DEG C, crushing the plating layers, and screening to obtain recovered steel balls and recovered plating layers. According to the method, through heat treatment, quenching and crushing in cooperation, the difference of thermal expansion coefficients between the plating layer and the steel ball is effectively utilized, plating layer stripping treatment and recycling of the plating layer steel ball are achieved, the surface flatness and roundness of the recycled steel ball are high, and the content of valuable metal in the recycled plating layer is high; the method is simple, efficient, low in energy consumption, low in cost and suitable for large-scale treatment.

Description

Technical Field

[0001] The invention belongs to the field of metal recovery, and in particular relates to a recovery and treatment method for steel balls. Background Art

[0002] Electroplating is an important link in the processing and production of tube shell porcelain, frame, etc. Among them, roller plating is a commonly used electroplating process in industrial production. This process mixes the product to be plated, steel balls and other conductive media with the plating solution, and electroplating is performed with the electroplating roller as the cathode and the plating solution as the anode. Among them, the steel ball not only has a low dielectric constant, but also has a large contact area with the plating solution, which can effectively promote the conductivity between the product to be plated and the plating solution, improve the discharge density and the electrodeposition rate of the coating. As the electroplating roller rotates, the steel ball is driven to roll, and the plating solution and the product are rolled and stirred, so that the additives and metal ions in the plating solution can be mixed, the electroplating quality of the product surface is improved, and the coating is more uniform. In addition, the steel ball can also be used as an abrasive to collide and grind the inclusions such as substances and oxides on the surface of the parts to be plated to improve the adhesion and flatness of the plated metal on the surface of the product. Based on the role of the above-mentioned steel ball, the steel ball is often called an electroplating auxiliary steel ball.

[0003] The guide steel balls used in electroplating will also be electroplated with metal during the electroplating process. After repeated use, the diameter of the steel balls gradually increases, and even exceeds the size requirements of the rolling process. In order to ensure the quality of the rolling plating process, large-sized steel balls will be screened out for scrapping, resulting in frequent loss of steel balls. The metal coating attached to the steel balls is often a high-value-added product. If appropriate methods can be adopted to recycle it, the production cost can be effectively reduced.

[0004] The commonly used stripping method is to recycle the metal coating on the surface of the guide steel ball. The recycling process uses the steel ball to be stripped as the anode and the anode metal plate of the electroplating line as the cathode. Through the action of the current, the metal coating on the surface of the steel ball is electrolytically transferred to the cathode block. However, this method has high energy consumption, long time, and is prone to electrolytic corrosion of the surface of the stainless steel ball, resulting in a rough surface of the recycled steel ball and a low roundness pass rate. In addition, the cathode metal coating deposited by electrodeposition is prone to contain impurities such as Fe, resulting in uncontrollable coating purity, which results in limited benefits for the recycled steel ball and coating. Summary of the invention

[0005] In view of the defects of the above-mentioned prior art related to the recovery of electroplating guide steel balls, the present invention will provide a method for recovering and processing the steel balls.

[0006] To achieve the above purpose, the following technical solutions are specifically included:

[0007] A steel ball recycling method comprises the following steps: subjecting the steel balls with coatings on their surfaces to a first-stage heat treatment, a second-stage heat treatment, quenching to 150-200°C, crushing the coatings, and screening to obtain recycled steel balls and recycled coatings.

[0008] In the method of the present invention, firstly, a two-step heating method is adopted to carry out heat treatment. In the first stage of heat treatment, the metal is preheated to the critical temperature of metal oxidation to ensure the uniformity of heating of the steel ball and the coating. Then, the temperature is rapidly raised to the second stage of heat treatment. The coating is broken by rapid heating to separate the coating and the steel ball, based on the principle that the thermal expansion coefficient of the internal steel ball is greater than that of the coating metal. The metal on the surface of the steel ball is attached to the surface of the steel ball in the form of electroplating and has a certain bonding force. Rapid heating helps the steel ball to expand and crack the coating, thereby destroying the bonding between the two. Secondly, quenching is directly carried out after the heat treatment, and the difference in thermal expansion coefficient between the coating and the steel ball is again used to separate the bonding part between the coating and the steel ball. The rapid cooling achieved by quenching is mainly to reduce oxidation caused by staying in the high temperature section, and to minimize the direct bonding and adhesion between the coating shell and the steel ball during rapid contraction, so as to facilitate peeling. Finally, the coating is crushed and screened to completely separate the steel ball and the coating. The present invention effectively utilizes the difference in thermal expansion coefficients between different metals through heat treatment, quenching and crushing, and realizes the coating stripping and recycling of coated steel beads. The method is simple, efficient, low in energy consumption and cost, and is suitable for large-scale processing.

[0009] Preferably, the steel ball with a coating on the surface is an auxiliary steel ball used in electroplating, and the steel ball includes a stainless steel ball.

[0010] Preferably, in the first stage of heat treatment, the temperature is 150-200° C., the heating rate is 50-100° C. / min, and the holding time is 1-2 min.

[0011] Based on the metal oxidation reaction temperature in the coating, the preheating temperature of the first stage is not higher than 200°C. When the temperature is too high, the coating stays near the oxidation temperature range for too long, resulting in increased oxidation of the coating and the steel ball, and some oxides are mixed into the valuable metals in the coating, reducing their purity. To improve the processing efficiency, the heating rate of the first stage heat treatment can be controlled above 50°C / min. A slow preheating rate will also cause the coating and the steel ball to be heated for too long, resulting in increased oxidation and reduced purity of the valuable metals in the coating. The preheating rate is generally not higher than 100°C / min, and is kept warm for 1 to 2 minutes. When it is too fast, it is easy to heat unevenly and the preheating effect cannot be achieved, resulting in part of the coating shell not being completely peeled off and the steel ball surface flatness being poor.

[0012] Preferably, in the second stage of heat treatment, the temperature is 450-700° C., the heating rate is greater than 150° C. / min, and the holding time is 1-5 min.

[0013] More preferably, in the second stage of heat treatment, the temperature is 500-600° C., the heating rate is 700-1000° C. / min, and the holding time is 2-3 min.

[0014] The heat treatment temperature in the second stage should be in the range of 450-700℃. When the temperature is too low, the steel balls are not fully heated, and the separation of the steel balls and the coating is not complete. When the temperature is too high, they are prone to oxidation and blackening. When the heating rate of the second stage heat treatment is greater than 150℃ / min, the coating is broken by rapid heating, using the principle that the thermal expansion coefficient of the internal steel balls is greater than that of the coated metal. When the heating rate is too low, the coating and the steel balls stay in the high temperature section for a long time, the metal is easily oxidized in the air atmosphere, the recovery efficiency of valuable metals is reduced, and the steel balls are oxidized and blackened, increasing the workload of subsequent cleaning. If the heat treatment time in the second stage is too short, some steel balls will not be fully heated and cannot break the coating. If the time is too long, the coating and the surface of the steel balls will be easily oxidized at high temperatures, reducing the recovery efficiency.

[0015] Preferably, the heating method of the first stage heat treatment and / or the second stage heat treatment includes but is not limited to at least one of high-frequency induction heating and high-temperature resistance wire heating.

[0016] Preferably, during the quenching, the cooling rate is 300 to 1200° C. / min.

[0017] When the cooling rate during quenching is slow, the steel ball stays in the high temperature section for a long time and is easily oxidized and blackened. When the cooling rate is fast, the strength of the steel ball material is reduced, resulting in the surface of the steel ball being easily worn and scratched when broken, making it poorly flat.

[0018] Preferably, after quenching to 150-200°C, the product is naturally cooled to room temperature; after quenching to 150-200°C, the product is dried at a temperature of 80-120°C for 1-4 hours.

[0019] In practical operation, it is found that when the temperature of the steel ball is not higher than 200℃, the thermal expansion and contraction of the steel ball is not obvious, and there is no oxidation and blackening. It can stay in the temperature range of 200℃ to room temperature appropriately, which can also effectively prevent the internal steel ball strength from being reduced due to excessive cooling, and avoid the surface of the steel ball being worn and scratched when it is broken, resulting in poor flatness.

[0020] Preferably, in the crushing of the coating, the crushing method used is pressure crushing, and the pressure crushing equipment includes jaw, double-roller, and disc crushers; research has found that if grinding crushing is used, the peeling effect is not good; if impact crushing is used, the steel balls are easily flattened; if stirring crushing is used, deep scratches are likely to occur, and the final crushing effect is not ideal.

[0021] Preferably, the mass percentage of valuable metal elements in the recovered coating is ≥98%.

[0022] Preferably, the mass percentage of impurities in the recovered coating is less than 2%.

[0023] The valuable metal elements referred to in the present invention include relatively high-value metal elements such as Ni, Sn, and rare earth metals. The impurities referred to in the present invention include elements such as Fe and Cr. Through the recycling method of the present invention, the recovered coating has a high content of valuable metals and a low content of impurities such as iron, which can improve the efficiency of recovering valuable metals in the coating.

[0024] Preferably, the surface roughness of the recycled steel balls is Ra<0.4 μm.

[0025] Preferably, the roundness qualification rate of the recycled steel balls is ≥98%.

[0026] Through the recycling method of the present invention, the obtained steel balls have high roundness qualification rate and surface flatness, which can improve the efficiency of recycling steel balls.

[0027] The present invention also provides an application of the steel ball recycling method in the recycling and utilization of electroplating process consumables. Through the recycling method of the present invention, not only the auxiliary steel balls in the electroplating process can be reused, but also the electroplating metal materials in the electroplating process can be reused, thereby improving the utilization value of the electroplating metal materials and increasing the benefits.

[0028] Compared with the prior art, the present invention has the following beneficial effects: in the steel ball recycling method of the present invention, the difference in thermal expansion coefficient between the coating and the steel ball is effectively utilized through heat treatment, quenching and combined with crushing, so as to realize the coating stripping and recycling of the coated steel ball, so that the surface flatness and roundness of the recycled steel ball are high, and the recycled coating has a high content of valuable metals; the method is simple, efficient, low in energy consumption, low in cost, and suitable for large-scale processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The figure is a flow chart of the steel ball recycling method of the present invention.

[0030] Figure 2 Schematic diagram of temperature changes in the first and second stages of heat treatment in the steel ball recycling method of the present invention. DETAILED DESCRIPTION

[0031] In order to better illustrate the purpose, technical scheme and advantages of the present invention, the present invention will be further described below through specific examples. The test methods used in the examples and / or comparative examples are conventional methods unless otherwise specified; the materials, reagents, etc. used can be obtained from commercial channels unless otherwise specified.

[0032] Example 1

[0033] A method for recycling steel balls comprises the following steps, and the flow chart is as follows: Figure 1 :

[0034] (1) The electroplated conductive stainless steel beads wrapped with a coating are placed in a heat treatment device and heat treated in two steps: the first stage and the second stage. The first stage of heat treatment is a preheating stage. The temperature change diagram of the two-step heat treatment is shown in FIG. Figure 2 The specific steps are as follows: first, the stainless steel beads are heated to 180°C (temperature 1) at a heating rate of 50°C / min (heating rate 1), and kept warm for 1.5 minutes (heating time 1), and the stainless steel beads and the coating are heated uniformly at a temperature lower than the metal oxidation temperature, and then the temperature is quickly raised to 550°C (temperature 2) at a heating rate of 300°C / min (heating rate 2) and kept warm for 2 minutes (heating time 2);

[0035] (2) After the heat treatment, the sample was directly taken out and quenched to 200°C at a cooling rate of 700°C / min, then naturally cooled to room temperature in air, and then dried at 90°C for 2h;

[0036] (3) Using pressure to crush the coating on the surface of the stainless steel beads, and controlling the particle size range of the crushed particles to be larger than the diameter of the internal stainless steel beads, and adjusting the minimum width of the discharge port to a width slightly larger than the diameter of the internal stainless steel beads for preliminary screening;

[0037] (4) Finally, the completely peeled steel balls and the coating shell powder are separated by sieving through a sieve to obtain recycled steel balls and recycled coatings.

[0038] Embodiments 2 to 5

[0039] Compared with Example 1, Examples 2 to 5 differ in that the heating rate 1 is different, as shown in Table 1, and the rest is the same.

[0040] Embodiment 6-7

[0041] Compared with Example 1, Examples 6 to 7 differ in that the temperature 1 is different, as shown in Table 1, and the rest are the same.

[0042] Embodiments 8 to 9

[0043] Compared with Example 1, Examples 8 to 9 differ in that the heat preservation time 1 is different, as shown in Table 1, and the rest is the same.

[0044] Embodiments 10 to 11

[0045] Compared with Example 1, Examples 10 to 11 differ in that the heating rate 2 is different, as shown in Table 1, and the rest is the same.

[0046] Embodiments 12 to 15

[0047] Compared with Example 1, Examples 12 to 15 differ in that the temperature 2 is different, as shown in Table 1, and the rest are the same.

[0048] Embodiments 16 to 18

[0049] Compared with Example 1, Examples 16 to 18 differ in that the insulation time 2 is different, as shown in Table 1, and the rest is the same.

[0050] Examples 19 to 22

[0051] Compared with Example 1, Examples 19 to 22 differ in cooling rates, as shown in Table 1, and the rest are the same.

[0052] Comparative Examples 1-2

[0053] The difference between Comparative Examples 1 and 2 and Example 1 is that the heating rate 1 is different, see Table 1 for details, and the rest is the same.

[0054] Comparative Examples 3-4

[0055] The difference between Comparative Examples 3 and 4 and Example 1 is that the temperature 1 is different, see Table 1 for details, and the rest is the same.

[0056] Comparative Examples 5-6

[0057] The difference between Comparative Examples 5 and 6 and Example 1 is that the holding time 1 is different, see Table 1 for details, and the rest is the same.

[0058] Comparative Example 7

[0059] Compared with Example 1, Comparative Example 7 differs in that the heating rate 2 is different, see Table 1 for details, and the rest is the same.

[0060] Comparative Examples 8 to 9

[0061] The difference between Comparative Examples 8 and 9 and Example 1 is that the temperature 2 is different, see Table 1 for details, and the rest is the same.

[0062] Comparative Examples 10-11

[0063] The difference between Comparative Examples 10 and 11 and Example 1 is that the holding time 2 is different, see Table 1 for details, and the rest is the same.

[0064] Comparative Examples 12-13

[0065] The difference between Comparative Examples 12 and 13 and Example 1 is that the cooling rates are different, see Table 1 for details, and the rest are the same.

[0066] Comparative Example 14

[0067] The difference between this comparative example and Example 1 is that in step (1), the first stage of heat treatment preheating process is not performed, and the temperature is directly increased from room temperature to 550°C at 300°C / min, and the rest is the same.

[0068] Comparative Example 15

[0069] The difference between this comparative example and Example 1 is that in step (2), instead of quenching to 200°C and then air cooling, the temperature is directly cooled from the heat treatment temperature of 550°C to room temperature at 700°C / min, and the rest is the same.

[0070] Table 1

[0071]

[0072]

[0073] Recycled steel balls and coating tests:

[0074] (a) Valuable metal element composition in the coating: The broken and detached coating samples were ultrasonically cleaned with alcohol and then dried. The element composition was tested using an energy spectrum scanning or full spectrum direct reading inductively coupled plasma optical emission spectrometer (ICP-OES).

[0075] The coating generally contains valuable metal elements (the specific element types are related to the specific electroplating process), O elements, etc. The valuable metal elements referred to in the present invention include metal elements with relatively high value such as Ni, Sn, and rare earth metals. Standard: The valuable metal content in the coating should be ≥98wt%, and the impurity elements such as Fe and Cr should be <2wt%. The purity of the coating is evaluated by the content of valuable metals in the coating. If the content of valuable metal elements in the coating is high, the purity of the coating is high. On the contrary, if the content of valuable metal elements in the coating is low, the purity of the coating is low.

[0076] (b) Surface roundness of stainless steel balls: 100 recycled stainless steel ball samples were taken and placed on a sample plate (the sample plate is a plastic plate with multiple hemispherical grooves, and the cross-section is the standard circle of stainless steel balls). The stainless steel balls and the round holes were observed and compared under a CCT imaging microscope to see whether they overlapped. Compliance standard: The proportion of stainless steel beads that can overlap should be ≥98%.

[0077] (c) Surface flatness of stainless steel balls: 100 samples of recycled stainless steel beads were taken and tested using a surface roughness measuring instrument; compliance standard: surface roughness Ra < 0.4 μm.

[0078] The test results are shown in Table 2.

[0079] Table 2

[0080]

[0081]

[0082] It can be seen from the above embodiments that the steel ball recycling method of the present invention can achieve the purpose of high purity of the recycled coating, low content of impurity elements such as iron and chromium, and high surface flatness and roundness pass rate of the recycled steel balls, wherein the valuable metal content in the recycled coating is ≥98wt%, and the impurity content is <2wt%; the surface roundness pass rate of the recycled steel balls is ≥98%, and the surface roughness Ra is <0.4μm.

[0083] It can be seen from Examples 1-5 and Comparative Examples 1 to 2 that when the preheating rate is too low, the oxidation degree of the coating and the stainless steel beads increases due to the long heating time, and some oxides are mixed into the valuable metals, reducing their purity; when the preheating rate is too high, due to uneven heating, part of the coating shell is not completely peeled off, resulting in poor flatness of the stainless steel beads.

[0084] It can be seen from Examples 1, 6 to 7 and Comparative Examples 3 to 4 that when the preheating temperature is too low, the outer coating shell of the stainless steel bead is not completely peeled off due to uneven heating, and the flatness of the stainless steel bead is poor; when the preheating temperature is too high, the oxidation degree of the coating and the stainless steel bead increases due to staying near the oxidation temperature range for too long, and some oxides are mixed into the valuable metals, reducing their purity.

[0085] It can be seen from Examples 1, 8 to 9 and Comparative Examples 5 to 6 that when the preheating and holding time is too short, due to uneven heating, part of the coating shell is not completely peeled off, and the surface flatness of the stainless steel bead is not good; when the preheating and holding time is too long, due to the long heating time, the metal is easily oxidized, and some oxides are mixed into the valuable metal, reducing its purity.

[0086] It can be seen from Examples 1, 10 to 11 and Comparative Example 7 that when the heating rate is too low, the oxidation degree of the coating and the stainless steel beads increases due to the long heating time, and some oxides are mixed into the valuable metals, which reduces their purity. In addition, the stainless steel beads have a slow thermal expansion rate and fail to break the coating in time, resulting in poor flatness and roundness of the stainless steel beads.

[0087] It can be seen from Examples 1, 12 to 15 and Comparative Examples 8 to 9 that when the second-stage heat treatment temperature is too low, the stainless steel beads cannot completely break through the coating due to limited thermal expansion, and part of the coating shell is not completely peeled off, resulting in poor surface flatness and roundness of the stainless steel beads; when the second-stage heat treatment temperature is too high, the coating and the stainless steel beads are easily oxidized and blackened, which increases the degree of oxidation of the coating and the stainless steel beads, increases the amount of oxides in the metal, and results in reduced coating purity and increased stainless steel bead flatness.

[0088] It can be seen from Examples 1, 16-18 and Comparative Examples 10-11 that when the heat treatment holding time is too short, the stainless steel beads are not heated sufficiently and the thermal expansion is limited, so the coating cannot be completely broken, resulting in part of the coating shell not being completely peeled off and the flatness and roundness of the stainless steel beads being poor; when the heat treatment holding time is too long, the oxidation degree of the coating and the stainless steel beads increases due to the long heating time, and some oxides are mixed into the valuable metals, which reduces the purity of the coating.

[0089] It can be seen from Examples 1, 19-22 and Comparative Examples 12-13 that when the cooling rate is too slow, the high temperature section residence time is too long, resulting in an increased degree of oxidation of the coating and the stainless steel beads, and some oxides are mixed into the valuable metals, which reduces the purity of the coating; when the cooling rate is too fast, the strength of the internal stainless steel beads is reduced, resulting in the surface of the stainless steel beads being easily worn and scratched when broken, resulting in poor flatness.

[0090] It can be seen from Example 1 and Comparative Example 14 that when heated directly from room temperature to 550°C, the stainless steel beads and the coating are not heated sufficiently due to the rapid heating without preheating, so that part of the coating shell is not completely peeled off, and the flatness and roundness of the stainless steel beads are not good.

[0091] It can be seen from Example 1 and Comparative Example 15 that when directly cooled from 550°C to room temperature, the strength of the internal stainless steel beads is reduced due to the excessively fast cooling rate, resulting in the surface of the steel beads being easily worn and scratched when broken, resulting in poor flatness of the stainless steel beads.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for recycling steel balls, characterized in that: The method comprises the following steps: subjecting steel balls with coatings on their surfaces to a first-stage heat treatment, a second-stage heat treatment, quenching to 150-200° C., crushing the coatings, and screening to obtain recycled steel balls and recycled coatings.

2. The method for recycling steel balls according to claim 1, characterized in that: In the first stage of heat treatment, the temperature is 150-200° C., the heating rate is 50-100° C. / min, and the holding time is 1-2 min.

3. The method according to claim 1, wherein: In the second stage of heat treatment, the temperature is 450-700°C, the heating rate is greater than 150°C / min, and the holding time is 1-5 min.

4. The method for recycling steel balls according to claim 3, characterized in that: In the second stage of heat treatment, the temperature is 500-600°C, the heating rate is 700-1000°C / min, and the holding time is 2-3min.

5. The method for recycling steel balls according to claim 1, characterized in that: In the quenching, the cooling rate is 300-1200° C. / min.

6. The method for recycling steel balls according to claim 1, characterized in that: After quenching to 150-200° C., the product is naturally cooled to room temperature; after quenching to 150-200° C., the product is dried at a temperature of 80-120° C. for 1-4 hours.

7. The method for recycling steel balls according to claim 1, characterized in that: The mass percentage of valuable metal elements in the recovered coating is ≥98%.

8. The method for recycling steel balls according to claim 1, characterized in that: In the crushing of the coating, the crushing method used is pressure crushing.

9. The method for recycling steel balls according to claim 1, characterized in that: The surface roughness of the recycled steel balls Ra is less than 0.4 μm; and the qualified rate of roundness of the recycled steel balls is ≥98%.

10. Use of the steel ball recycling method according to any one of claims 1 to 9 in recycling and reusing electroplating process consumables.

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